Add a switch to invert web contents (non-accel only).

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index bbc4eccc3adcab50a70ab255b7c9d83ab21e32e5..99b3731082e9003987ed98ecaff36bf65388ec56 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -24,6 +24,7 @@
 #include "ipc/ipc_sync_message.h"
 #include "skia/ext/platform_canvas.h"
 #include "third_party/skia/include/core/SkShader.h"
+#include "third_party/skia/include/effects/SkTableColorFilter.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebCursorInfo.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/platform/WebPoint.h"
 #include "third_party/WebKit/Source/WebKit/chromium/public/WebPopupMenu.h"
@@ -98,7 +99,8 @@ RenderWidget::RenderWidget(WebKit::WebPopupType popup_type)
       is_accelerated_compositing_active_(false),
       animation_update_pending_(false),
       animation_task_posted_(false),
-      invalidation_task_posted_(false) {
+      invalidation_task_posted_(false),
+      invert_(false) {
   RenderProcess::current()->AddRefProcess();
   DCHECK(RenderThread::Get());
   has_disable_gpu_vsync_switch_ = CommandLine::ForCurrentProcess()->HasSwitch(
@@ -217,6 +219,7 @@ bool RenderWidget::OnMessageReceived(const IPC::Message& message) {
     IPC_MESSAGE_HANDLER(ViewMsg_Repaint, OnMsgRepaint)
     IPC_MESSAGE_HANDLER(ViewMsg_SetTextDirection, OnSetTextDirection)
     IPC_MESSAGE_HANDLER(ViewMsg_Move_ACK, OnRequestMoveAck)
+    IPC_MESSAGE_HANDLER(ViewMsg_InvertWebContent, OnInvertWebContent)
     IPC_MESSAGE_UNHANDLED(handled = false)
   IPC_END_MESSAGE_MAP()
   return handled;
@@ -587,6 +590,16 @@ void RenderWidget::PaintRect(const gfx::Rect& rect,
   canvas->translate(static_cast<SkScalar>(-canvas_origin.x()),
                     static_cast<SkScalar>(-canvas_origin.y()));
 
+  if (invert_) {
+    // Draw everything to a temporary bitmap and then apply an
+    // inverting color map to the result. This is balanced by an extra
+    // call to canvas->restore(), below.
+    DCHECK(invert_paint_.get());
+    SkRect bounds;
+    bounds.set(rect.x(), rect.y(), rect.right(), rect.bottom());
+    canvas->saveLayer(&bounds, invert_paint_.get());
+  }
+
   // If there is a custom background, tile it.
   if (!background_.empty()) {
     SkPaint paint;
@@ -647,6 +660,9 @@ void RenderWidget::PaintRect(const gfx::Rect& rect,
     skia::GetTopDevice(*canvas)->accessBitmap(false);
   }
 
+  if (invert_)
+    canvas->restore();
+
   PaintDebugBorder(rect, canvas);
   canvas->restore();
 }
@@ -1389,6 +1405,37 @@ void RenderWidget::OnSetTextDirection(WebTextDirection direction) {
   webwidget_->setTextDirection(direction);
 }
 
+void RenderWidget::OnInvertWebContent(bool invert) {
+  if (invert_ == invert)
+    return;
+
+  invert_ = invert;
+
+  if (invert_ && !invert_paint_.get()) {
+    // Gamma-aware color inversion: each source pixel value x is normally
+    // displayed on a computer monitor with a gamma correction x^gamma,
+    // where gamma is typically in the range 1.8...2.2. By approximating
+    // gamma as exactly 2, the formula to invert one value is sqrt(1 - x^2).
+    uint8_t table[256];
+    for (unsigned int i = 0; i < 256; i++) {
+      double value = i / 255.0;
+      value = sqrt(1 - (value * value));
+      table[i] = static_cast<uint8_t>(255 * value);
+    }
+
+    // Create a Skia Paint with this inverting color map.
+    invert_paint_.reset(new SkPaint());
+    invert_paint_->setStyle(SkPaint::kFill_Style);
+    invert_paint_->setColor(SK_ColorBLACK);
+    SkColorFilter* filter = SkTableColorFilter::CreateARGB(
+        NULL, table, table, table);
+    invert_paint_->setColorFilter(filter);
+    filter->unref();
+  }
+
+  OnMsgRepaint(size_);
+}
+
 webkit::ppapi::PluginInstance* RenderWidget::GetBitmapForOptimizedPluginPaint(
     const gfx::Rect& paint_bounds,
     TransportDIB** dib,